2051938 - Port Bug 2051196 - Add a global [hidden] { display: none !important } rule instead of :not([hidden]) display guards

Status: RESOLVED FIXED

(Thunderbird :: Upstream Synchronization, defect, P5)

Description

[Treeherder Bug Filer]

Filed by: john [at] thunderbird.net

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Comment 1

[John Bieling]

Attachment: Bug 2051938 - Make the hidden attribute authoritative for visibility after bug 2051196's global [hidden] rule. r=#thunderbird-reviewers

Bug 2051196 added a global :where([hidden]) { display: none !important }
rule to the shared toolkit stylesheets Thunderbird loads (global-shared.css,
in-content/common-shared.css, findbar.css). This makes the hidden attribute
authoritative: a plain (non-!important) display: rule can no longer reveal an
element that carries hidden. Several Thunderbird widgets relied on exactly
that, so they were left stuck hidden.

Fix each by letting the hidden attribute drive visibility, keeping CSS
display for layout only:

• Folder tree TLS-error status icon: the button carries hidden in markup and
  was shown via .tls-error > .status-icon { display: unset }. Toggle
  row.statusIcon.hidden in the show-tls-error / server-connection-succeeded
  handlers instead, and drop the display: unset override.

• Findbar: the <lazy-findbar> wrapper is a transparent display: contents
  layout passthrough; the inner <findbar> owns visibility (and hides itself via
  visibility: collapse so it can animate). Stop toggling the wrapper's own
  hidden attribute in the setter and drop hidden="true" from the markup, so
  the global rule can't display: none the wrapper and kill the findbar. The
  wrapper's open/closed state is still reported from the inner findbar.

• Account hub branding header: no production change. #brandingHeader is
  correctly hidden by default and shown per step via showBrandingHeader(); the
  bug just made that gate actually work. The two header tests were relying on
  the previous always-visible behaviour, so they now call showBrandingHeader()
  the same way the step widgets do.

A tree-wide audit found no other instances of the anti-pattern; comm elsewhere
already uses :not([hidden]) guards or pure-attribute visibility.

Comment 2

[John Bieling]

Attachment: Bug 2051938 - Restore account hub header branding and window controls after bug 2051196. r=freaktechnik

Bug 2051196's global :where([hidden]) { display: none !important } makes the
hidden attribute win over author display rules. The account hub header relied
on the old behaviour in two spots:

• The first-run welcome branding lives in #brandingHeader, which is shown per
  step via showBrandingHeader(). The initial email-auto-form step never called
  it -- it only appeared before because branding was always visible -- so on
  first run the welcome text stayed hidden. Call showBrandingHeader() from its
  connectedCallback, like the other steps already do.

• The close and minimize buttons were nested inside #brandingHeader, so they
  vanished on every step that doesn't show branding (and the dialog could no
  longer be closed from those steps). Move #headerButtonsContainer out to be a
  direct child of #accountHubHeader so the window controls are always present.
  Applied to the header template and the account hub test fixtures.

The first-run header test now calls showBrandingHeader() to exercise the
branding the same way the steps do.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/comm-central/rev/51ced801b91c
Make the hidden attribute authoritative for visibility after bug 2051196's global [hidden] rule. r=freaktechnik
https://hg.mozilla.org/comm-central/rev/5c103155a04e
Restore account hub header branding and window controls after bug 2051196. r=freaktechnik

Comment 4

[Intermittent Failures Robot]

1 failures were associated with this bug in the last 7 days.

Repository breakdown:

• comm-central: 1

Table

	no_variant
linux2404-x86_64/opt	1

For more details, see:

https://treeherder.mozilla.org/intermittent-failures/bugdetails?bug=2051938&startday=2026-06-29&endday=2026-07-05&tree=all